1. Field of the Invention
This invention relates to disk drive suspensions, and more particularly, to improvements in the manufacture of disk drive suspension interconnects to secure better electrical grounding of suspension components such as copper circuit layers to grounded portions of the suspension such as stainless steel layers, to enable increased numbers of copper circuit layers, and further relates to suspension products thus manufactured. In particular, a method is provided to connect the copper circuitry of a component such as a slider with the stainless steel part of the suspension interconnect using vias modified in manufacture to have better electrical connection than available heretofore. In one aspect, the invention provides optimal performance in hard disk drive sliders by improving the electrical grounding thereof through a via having a copper conductor bonded to a stainless steel layer using a tie layer of chromium and optionally a copper flash layer as well.
2. Description of the Related Art
Disk drive suspension interconnects, such as Integrated Lead Suspensions (ILS) for hard disk drives typically have three layers, including a stainless steel foil that provides mechanical properties for the suspension, two or more conductive traces comprising gold plated, patterned copper conductive circuits paths that provide the electrical connection between the read/write head slider and the termination pads of the suspension, and a dielectric layer that provides electrical insulation between the stainless steel foil and the conductive traces.
It is known to be desirable to ground various components of a disk drive suspension such as the body of the read/write head slider. One of the major challenges in the design of hard disk drive suspensions is attaining a suitable, reliable grounding connection between the conductive copper traces connected electrically to the slider and the underlying stainless steel foil layer given the limited space available to make the connection. The difficulty of bonding to stainless steel and dissimilarity of the metals (Cu, Au, SST) pose additional significant challenges to creating a reliable grounding of the slider, but reliable grounding is essential to maintaining the signal fidelity between the read/write head and amplifier.
Among the prior art approaches to solving the slider grounding problem is creating a hole in the dielectric between the slider and the stainless steel foil, typically 25 μm deep, and filling the hole with conductive adhesive to provide an electrical connection between the slider and the stainless steel. This approach is deficient, however, since conductive adhesive connections are typified by very high interconnect resistance resultant from the passive (self-healing) nature of the stainless steel and the lack of a conductive, fully metallic bond between the steel layer and the conductive adhesive. High interconnect resistance limits the quality of the electrical connection to ground and thus slider performance dependent on a good grounding is degraded.
Another approach to slider grounding uses a spanning lead that extends from the slider, beyond the edge of the dielectric layer and opposite the stainless steel layer where it is subsequently bent over onto the stainless steel layer and electrically and mechanically affixed there, using, typically, a conductive polymer. Spanning leads are very fragile and can be easily mis-bent during manufacture causing lowered manufacturing yields. Further, even if perfectly accomplished, the process of physically bending and adhering leads to the stainless steel suspensions is a very labor-intensive process that does not lend itself to high-volume, low-cost manufacturing, such as simultaneous gang bonding of multiple suspensions.
In both of these prior art processes the presence of conductive adhesives can cause increased drive contamination that may adversely affect drive reliability, and their use is environmentally undesirable for workers.